Lockboxes are commonly used in the real estate sales industry to provide means for a large number of salesmen to gain access to a locked building. The lockbox is secured to the building and contains a key fitting a lock controlling access to the building. The lockbox key repository is typically secured with a combination lock. A common variety of combination lock used for lockboxes, briefcases, suitcases and even bicycle locks employs a series of rotatable tumbler rings. The rings have a series of numbers, letters or other characters inscribed on them and the alignment of the tumbler rings with the correct combination of such characters will allow the lock to be opened. With most locks of this nature, after the lock has been closed, usually by sliding a button or closing a hasp, the opening combination will still remain visible on the tumbler rings. Unless the user of the lock is careful to scramble the combination, the lock may be easily opened again by any unauthorized person. The present invention addresses this problem by providing a means for the combination to be scrambled automatically upon closing of the lock mechanism.
A number of combination lock designs have been developed that attempt to solve this problem. U.S. Pat. No. 4,910,981 issued to Gartner discloses an automatically self locking and self scrambling combination lock wherein a spring biased bolt is moveable by its bias toward a locking position and a detent is provided on an end of the fence arm associated with a fence lever connected to the bolt whereby on movement of the bolt towards its locking position, the detent engages the edge of a single one of the tumbler wheel gates to scramble that tumbler wheel alignment relative the other tumbler wheels as the fence arm leaves the tumbler wheel gates. Additional spring means are provided in the form of a multiple armed spring member having a first spring arm which urges the fence lever toward the tumbler wheels when the spring member is deflected under the action of an actuator roller once on each rotation of an associated lock shaft, a second spring arm which normally urges the fence lever away from the tumbler wheels when the spring member is not deflected and a third spring arm which normally biases the spring member toward its non-deflected position of rest. In addition, an eccentric roller rim associated with the actuator roller for deflecting the spring member is provided so that the timing of such defective movement of the spring member in response to rotation of the lock shaft varies from rotation to rotation in response to incremental movements of the eccentric rim about its mounting post as it goes through successive engagements with the spring member.
U.S. Pat. No. 4,343,163 issued to Scelba et al. describes a combination lock of the dial and sleeve type that has a scramble feature enabling a hasp to be engaged with a latch of the lock even when the dials and sleeves are not on-combination, by independent movement of the latch relative to manual actuating means of the lock. When the hasp is engaged, it supports the latch in a position in which the latch is adapted to engage a blocking element that prevents the latch from being moved out of its hasp-engaging position independently of the manual actuator. This arrangement effectively prevents the lock from being forced open when the hasp is engaged.
U.S. Pat. No. 7,290,417 issued to Huang describes a suitcase lock that can be opened either by setting a combination or by a key, in which dials of a suitcase lock are disposed with sleeves, and characterized in that a key tumbler is additionally fitted to the suitcase lock, and tongues located at a lower portion of a swing plate clamp connect to a slider. A groove at one end of the slider enables a push rod of the key tumbler to be clamped therein, and sloping grooves defined on another end enable the tongues of the swing plate to displace therein. In general, dials are used to control cuttings or circular arcs on the sleeves to operate the swing plate and hooking to a locked object and realize opening and closing of the lock. However, when in a locked state, without moving the dials, a key can be used to directly activate the key tumbler to push the slider, and thereby causes the swing plate to tilt in an opposite direction and the stopper at one end of swing plate can release the locked object from hooking position, thus opening the lock or suitcase.
U.S. Pat. No. 7,254,971 issued to Ruan describes a combination lock includes a lock body, a locking latch, a numerical actuation unit including a plurality of number rotors and a plurality of locking rings, and a password reset unit. The password reset unit includes a reset driver slidably extended at the lock body to couple with the locking rings, wherein when the reset driver is moved to drive the locking rings to slidably disengage with number rotors, the number rotors are free to rotate on the lock body to reset a new number-combination, such that when the reset driver is released that the locking rings are slidably returned back within the number rotors, the detachable end of the locking latch is unlocked once the number rotors are rotated at the new number-combination.
U.S. Pat. No. 7,216,518 issued to Shao discloses a mechanical dial combination lock for use in safes, file cabinets, security doors, vaults and warehouse doors. The disk type mechanical combination lock features a plurality of annular code discs, a base disc, a latch, an unlatching mechanism, a positioning mechanism, a dialing mechanism, a repositioning mechanism, a code-detecting mechanism, a casing and a dial. The dial combination lock is easily operated by persons familiar with conventional dial-face type combination locks, and yet is may be operated faster, and permits the combination code to be easily changed to any of a greater number of possible code combinations.
U.S. Pat. No. 7,047,772 issued to Yu describes a cable lock includes a case having a slot defined through a first side and an opening defined through the second side and being in communication with the slot. A flexible cable has one end fixed to the case and a free end of the flexible cable is removably engaged with the opening and the slot. A combination unit is received in the case includes a shaft movably extending through the combination unit. A top plate is connected to a top of the shaft and has a stop plate which is located inside of the second side and movably blocks the opening. A button is pivotably connected to the case and drives an action plate to push the top plate and the shaft downward so as to remove the stop plate away from the opening, and the free end of the flexible cable is able to remove from the opening.
U.S. Pat. No. 6,813,912 issued to Ng et al. describes a secure lockbox that includes an interior key lock controlling access to the mechanism for setting and changing the combination for the lock controlling access to the interior storage compartment of the lockbox. A second key lock controls the attachment bail of the lockbox, preventing unauthorized removal of the lockbox. The two key locks may be identically keyed. In a variant of the invention, a second combination lock controls the attachment bail instead of a key lock. Resilient coverings are provided for the attachment bail and the sides of the lockbox body to prevent damage to buildings and fixtures. A chain is provided to secure the door of the lockbox to the body. A slide latch having non-slip features is controlled by the door's combination lock and engages an edge of the door opening to secure the door opening.
It is an objective of the present invention to provide a combination lock suitable for use with a lockbox for use in the real estate sales industry. It is another objective to provide a combination lock that automatically scrambles the combination used to unlock the lock. It is a further objective to provide a combination lock that turns the lock tumbler rings to a different combination each time the lock is locked. It is a still further objective of the invention to provide means to control access to the setting of the combination for the lock. It is a final objective to provide a combination lock that may be easily used, is rugged and reliable and that may be inexpensively manufactured and maintained.
While some of the objectives of the present invention are disclosed in the prior art, none of the inventions found include all of the requirements identified.